It is interesting to note that Bukhari wrote a book about
the narrators (Zuafa-us-sagher). What is even more interesting is that Bukhari's
book condemns several narrators including: ... Saeed bin Urwa ... as
unreliable. However, the Hadith-collection of Bukhari in the its modern form
actually includes many traditions narrated by these very individuals! Obviously,
these traditions, which Bukhari rejected, were inserted in his book following
his death.

a narrator called "Saeed bin Urwa".

1. Did Al-Bukhari Say Said B. Urwa "Unreliable"?

It is interesting to note that there is no Said bin Urwa in Kitab
al-Du`afa al-Saghir. So, al-Bukhari could not have
called a non-existing narrator "unreliable".

The closest sounding name that we have come across is a Sa`id
bin Abi `Arubah. Al-Bukhari says:

138 - Sa`id Ibn Abi `Arubah: Abi `Arubah's
name is Mahran, the freed slave of Banu `Udayy Ibn Yashkur al-Basri
[i.e., from Basrah].
I heard Abu Nu`aym say: I recorded from him two hadiths after he became
confused.

Muhammad told us, Ahmed Ibn
Hanbal told us, Yahya told us: I asked Isma`il about a hadith
from Ibn Abi `Arubah concerning "Man does not become junub", he
did not know it.

Ahmed said: `Abd al-A`la narrated
to us from Sa`id from Isma`il from Ibn `Abbas his saying: "Four things
do not cause janabah" but he did not know it.

Muhammad told us, Ahmed said:
Quraush Ibn Ahmed told us: Sa`id Ibn Abi `Arubah swore to me that he had never
written anything from Qatadah. But Abu Ma`shar wrote to him asking him to
write the tafsir of Qatadah for him. He said: He wants to write the
tafsir on my authority.[1]

In the footnotes we read:

138 - He was the imam of the people
of al-Basrah in his time and has several writings but he changed near
the end [of his life] and was accused of [suspect opinions on] predestination.
Ibn Ma`in said, Yahya al-Qattan said: When I hear anything from
Shu`bah or Hisham or Ibn Abi `Arubah I don't pay attention except for
what I hear from his companions because they are trustworthy [Arabic: thiqah].
Ibn Ma`in also said: Sa`id became confused after the defeat of Ibrahim Ibn
`Abd Allah. Ahmed accused him of tadlis [i.e., deceit]. Ibn `Udayy
said: Sa`id is trustworthy and has many writings and whoever heard from him
after he became confused cannot be trusted. He died in 156 AH and the defeat
of Ibrahim was in 145 AH. [al-Mizan 151/2; al-Kabir 504/3][2]

Al-Bukhari says in his Kitab al-Tarikh
al-Kabir:

1679 - Sa`id Ibn Abi `Arubah, [his
kunyah is] Abu al-Nadr. Abi `Arubah's name is Mahran, a freed slave
of Banu `Udayy Ibn Yashkur, al-Basri. `Abd al-Samad said: He
died in 156 AH. Hafs Ibn `Umar said: He died three years before
al-Dustuwa'i [vowels?]. Abu Nu`aym said: I wrote from him two hadiths
after he became confused. He heard from al-Nadr Ibn Anas.[3]

Ibn Hajar in his Taqrib al-Tahdhib
said:

226 - Sa`id Ibn Abi `Arubah, Mahran
of Yashkur, their freed slave, [called] Abu al-Nadr al-Basri.
He is thiqah [trustworthy] and hafidh.
He has several writings but he's done much deceit and he became confused.
He was amongst the soundest people about Qatadah....[4]

To sum up the discussion on Sa`id bin Abi `Arubah, he was also
a narrator who was reliable except that in later life he made mistakes in his
hadith. So, if we find someone reporting from him when he was young and
reliable then there is no problem in accepting those hadith. Al-Bukhari
ensured that this condition was met before including his hadith in his
Sahih
as suggested by his own statements in Kitab al-Tarikh
al-Kabir and Kitab al-Du`afa al-Saghir.

2. Traditions Of Sa`id Bin Abi `Arubah
In The Sahih Of Al-Bukhari

Al-Bukhari narrated through him 101 hadiths. We produce
two of his hadiths with the isnad bundles and they are representative
of the rest.

The sister of Ma`qil bin Yasar was married to a man and
then that man divorced her and remained away from her till her period of the
'Iddah expired. Then he demanded for her hand in marriage, but Ma`qil got
angry out of pride and haughtiness and said, "He kept away from her when he
could still retain her, and now he demands her hand again?" So Ma`qil disagreed
to remarry her to him. Then Allah revealed: 'When you have divorced women
and they have fulfilled the term of their prescribed period, do not prevent
them from marrying their (former) husbands.' (2.232) So the Prophet sent for
Ma`qil and recited to him (Allah's order) and consequently Ma'qil gave up
his pride and haughtiness and yielded to Allah's order. [Kitab al-Talaq,
No. 4915]

The isnad bundle of this hadith is given below:

The hadith is narrated by Ma`qil b. Yasar as well as Al-Hasan
b. Abi al-Hasan and al-Bukhari collected it from both through isnads
that are independent of Sa`id bin Abi `Arubah.

Again, as it can be seen, al-Bukhari and others have collected
the above mentioned hadith from isnads that are independent of
Sa`id bin Abi `Arubah. Other examples can be seen in hadith no. 1899
in Kitab al-I`tikaaf, hadith no. 3410
in Kitab al-Riqaaq and hadith no. 78
in Kitab al-`Ilm.